Domain Authentication Slow when IP range / subnet different then DC

I am having issues with what I think is Domain Authentication slowing down some client software. The issue on happens when using Intergrated Authentication with SQL server. There is a lot happening so I will explain what happened to get to this point.

Every thing was working fine prior to the next things.

We had three DC's in our domain. One is a new machine Server 2008 r2 64bit, the other two have been in service for 4 years, Server 2003, 32 bit.

We de-promoted on of the older DC last night. It also was a DHCP and DNS Server. Those functions had been migrated to the new server about a week ago with no issue.

Our network has three ip ranges 192.168.2.x 192.168.3.x and 10.192.21.x.

All DC are on 192.168.2.x subnet. All client PC on this subnet work fine.

If I take a client PC that is in the 192.168.3.x subnet and try to access SQL (in 192.168.2.x subnet) every operation takes about 10-30 seconds per DB call.

If I switch from Intergrated Authenticaion to a saved password the app runs at normal speed.

If I access an internal website that is in the 2.x subnet with the PC while it is on the 3.x subnet the website is fast as it usually is.

If I move the client NIC cable to a port on the same switch (we have Cisco with a three VLans) and it is in the 2.x subnet, everything runs at normal speed.

I don't see any issues in the event viewer of the DC's, the client PC, or the SQL Server Box.

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You may just have to flush the dns for each PC--the router tables may also have a path in memory, a path that has no changed and so it is going to the old server first and then when it does not find the DHCP it goes to the new DHCP server. You may have to turn your router/switches off or force a refresh. On the PCs you can try IPCONFIG from a command prompt ipconfig /? will display help message
I would try ipconfig /all to see what the configuration information is
The try ipconfig /flushdns followed by ipconfig /registerdns. See below for details.
/release Release the IP address for the specified adapter.
/renew Renew the IP address for the specified adapter.
/flushdns Purges the DNS Resolver cache.
/registerdns Refreshes all DHCP leases and re-registers DNS names
/displaydns Display the contents of the DNS Resolver Cache.
/showclassid Displays all the dhcp class IDs allowed for adapter.
/setclassid Modifies the dhcp class id.

If DNS resolution fails, then the system will go to a broadcast mode for resolution of the name to IP address. Crossing subnets is an issue for broadcast resolution, causing a delay. I think your issue has to do with name resolution; something hasn't been updated with the new address - it could be server, client, or network component related. Managed Switches and Routers have "helper"s that all the passing of certain traffic that does not normally cross over subnets.

Managing application connectivity and security policies can be achieved more effectively when following a framework that automates repeatable processes and ensures that the right activities are performed in the right order.

I assume there is a configuration change needed within SQL to start using the new DC, but I have no idea what it would be. I know little about SQL; I'm lucky I know how to spell SQL.

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pamsautoAuthor Commented: 2013-12-06

I found the issue. The DNS Settings were wrong on the old DC and it was pointing at the non existent DNS server. I had assumed that the DC was pulling its config from a reservation in the DHCP server, but it was not, it was configured on the DC itself....

Grrr.. Thanks for the help. I am splitting the points because you both pointed me in the same direction.